linux-kernel - Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition

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Date:	Fri, 24 Jul 2015 11:34:45 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<linux-kernel@...r.kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<ian.campbell@...rix.com>, <linux-arm-kernel@...ts.infradead.org>,
	<stefano.stabellini@...citrix.com>
Subject: Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition

On 24/07/15 10:51, Julien Grall wrote:
> On 24/07/15 10:48, David Vrabel wrote:
>> On 24/07/15 10:39, Julien Grall wrote:
>>> Hi David,
>>>
>>> On 24/07/15 10:28, David Vrabel wrote:
>>>> On 09/07/15 21:42, Julien Grall wrote:
>>>>> The Xen hypercall interface is always using 4K page granularity on ARM
>>>>> and x86 architecture.
>>>>>
>>>>> With the incoming support of 64K page granularity for ARM64 guest, it
>>>>> won't be possible to re-use the Linux page definition in Xen drivers.
>>>>>
>>>>> Introduce Xen page definition helpers based on the Linux page
>>>>> definition. They have exactly the same name but prefixed with
>>>>> XEN_/xen_ prefix.
>>>>>
>>>>> Also modify page_to_pfn to use new Xen page definition.
>>>>>
>>>>> Signed-off-by: Julien Grall <julien.grall@...rix.com>
>>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>>>>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>>>>> Cc: David Vrabel <david.vrabel@...rix.com>
>>>>> ---
>>>>>     I'm wondering if we should drop page_to_pfn has the macro will likely
>>>>>     misuse when Linux is using 64KB page granularity.
>>>>
>>>> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
>>>> front/back drivers never deal with PFNs only GFNs.
>>>
>>> What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my
>>> series have them.
>>
>> I suggesting that you introduce these.
> 
> It's still not clear to me what you are suggesting here... Do you
> suggest to rename xen_pfn_to_page and xen_page_to_pfn by xen_gfn_to_page
> and xen_page_to_gfn?

Effectively, yes but it would be better to think that:

PFNs index guest-sized pages (which may be 64 KiB).

GFNs index Xen-sized pages (which is always 4 KiB).

David
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